In the refinishing field, putty compositions are often employed as part of the process of repairing deformities, such as scratches and/or depressions in automobile body parts. In such processes, the putty composition is often applied to the deformity, cured, sanded and finished with suitable painting steps to complete the refinish process.
At least partly due to improved efficiencies achieved by reduced curing times, putty compositions (sometimes identified as filler compositions) that are curable by ultraviolet radiation have been proposed. For example, U.S. Pat. No. 4,668,529 (“the '529 patent”) discloses a composition that can be cured in less than approximately five minutes when subjected to relatively high intensity ultraviolet radiation. The composition disclosed in the '529 patent includes a specific mixture of an epoxy resin, a di-functional acrylate cross-linking agent, a tri-functional acrylate cross-linking agent, a photoinitiator, an accelerator, dioctyl phthalate, and a filler, such as calcium sulfate dihydrate.
In another example, U.S. Pat. No. 6,312,765 (“the '765 patent”) discloses a putty composition that can be cured in about 30 to 60 seconds using an apparatus equipped with a 1.2 kW metal halide lamp. The putty compositions disclosed in the '765 patent include a specific mixture of an ultraviolet polymerizing prepolymer, an ultraviolet polymerizing monomer, an ultraviolet polymerizing initiator, and an extender pigment, such as calcium carbonate, barium sulfate, clay, talc, tonoko, white-carbon, and balloon.
One drawback of prior art putty compositions that are curable by ultraviolet radiation, such as those described above, is that they require the use of a relatively high intensity ultraviolet radiation source, such as the 1.2 kW metal halide lamps mentioned earlier, to effect adequate cure of the composition in a reasonable period of time, while achieving acceptable properties, such as sanding, adhesion and humidity properties. The use of such high intensity radiation equipment, however, has some drawbacks. For example, higher intensity radiation equipment, such as the lamps mentioned earlier, is larger and more difficult to handle than lower intensity equipment. Moreover, high intensity radiation equipment is more expensive to purchase and also more expensive to operate because they consume more energy than low intensity radiation sources. In addition, the use of high intensity ultraviolet radiation is undesirable in many situations because of the possibility of human exposure. Exposure to high intensity ultraviolet radiation is more harmful to humans than exposure to lower intensity ultraviolet radiation.